[Bug c/69002] C front end should warn about undefined access to atomic structure or union

[fw at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=69002

--- Comment #2 from Florian Weimer <fw at gcc dot gnu.org> ---
(In reply to Martin Sebor from comment #1)
> I actually wouldn't want to see GCC start issuing warnings for this code
> because it has well-defined semantics there.

Unfortunately, the generated code is truly abysmal, for example:

read1:
        pushq   %rbp
        movq    %rsp, %rbp
        movl    %edi, -32(%rbp)
        movl    -32(%rbp), %eax
        movl    %eax, -4(%rbp)
        movl    -4(%rbp), %eax
        popq    %rbp
        ret

read2:
        pushq   %rbp
        movq    %rsp, %rbp
        movq    %rdi, -24(%rbp)
        movq    -24(%rbp), %rax
        movl    (%rax), %eax
        movl    %eax, -4(%rbp)
        movl    -4(%rbp), %eax
        popq    %rbp
        ret

> initialized using one of the ATOMIC_VAR_INIT() or atomic_init() macros

I don't see this qualification in 6.5.2.3/5.  I don't think this issue is
touched in your blog post at all.